Negative phots when colours are inverted

Hi,

Trying to help a friend who is visually impaired. She sets her MacBook Pro to use inverted colors. Wondering if anyone has figured out a way to switch the photos in iPhoto back to normal while still in inverted mode? I can't see a way to do that.

What about 3rd party s/w or a web service like Flickr? She is an artist who paints from her photos. Any help and/or suggestions very much appreciated.

Regards,

Brian